man/man2/close.2: CAVEATS: Document divergence from POSIX.1-2024

man/man2/close.2: CAVEATS: Document divergence from POSIX.1-2024

POSIX.1-2024 now mandates a behavior different from what Linux (and many
other implementations) does.  It requires that we report EINPROGRESS for
what now is EINTR.

There are no plans to conform to POSIX.1-2024 within the Linux kernel,
so document this divergence.  Keep POSIX.1-2008 as the standard to
which we conform in STANDARDS.

Link: <https://sourceware.org/bugzilla/show_bug.cgi?id=14627>
Link: <https://pubs.opengroup.org/onlinepubs/9799919799/functions/close.html>
Cc: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Rich Felker <dalias@libc.org>
Cc: <linux-fsdevel@vger.kernel.org>
Cc: <linux-api@vger.kernel.org>
Cc: <libc-alpha@sourceware.org>
Signed-off-by: Alejandro Colomar <alx@kernel.org>